130
E. D. 5. CORNER AND ANTHONY 0 . DAVIES
B. Detritus
This fraction of the particulate material in the sea contains no
living plants or animals but includes bacteria, the faecal pellets and
cast moults of zooplankton and disintegrated phytoplankton cells.
Its capture by zooplankton has been deduced from examination of gut
contents. For example, Macdonald (1927) found that the guts of small
specimens of Meganyctiphanes norvegica (M. Sars) contained both
diatoms and I ‘ wet dust ”, i.e. flocculent detritus ; and Mauchlinc
(1960) found 20% by volume of “ grit ” and vegetable detritus in the
guts of Calanus jinmarchicus (Gunnerus) from deep water (150 m) in
the same sea area.
If detritus were a valuable diet for zooplankton, a large source of
food would be available to the animals, for Jsrgensen (1966) concludes
that of the total particulate material present in the sea generally only
10-20% by weight is represented by phytoplankton. However, the
nutritive value of detritus is by no means well established. Thus, so
far the only “ natural ” detritus tested is that obtained by Baylor and
Sutcliffe (1963), using material extracted from sea water by the action
of rising bubbles. The test animal was Artemia salina and the growth
rate of animals fed on detritus was compared with that of controls
either starved or fed on yeast. For the first four days animals given
detritus or yeast as a food had roughly the same growth rate, after
which that of animals fed on detritus was lower, although they continued to increase in size until the end of the sixteenth day. No measurements were made of the relative levels of the two diets, however, and to
establish the presence of dietary factors needed for reproduction would
require a much longer study, including attempts to rear the animals
through several generations. Moreover, Paffenhtifer and Strickland
(1970), studying an animal more representative of marine zooplankton,
found that natural detritus is not eaten by Calanus helgolandicus
(Claus), although the animal will apparently eat disintegrated samples
of its own faecal pellets, as well as “ dead ’’ diatom cells. It would be
interesting to know whether these two ingested forms of detritus have
any nutritive value.
C . Dissolved organic material
Putter (1909) was the first to claim that organic substances dissolved
in sea water may be absorbed and used by animals directly. However,
it has since become clear, mainly through the work of Moore et al.
(1912) and Krogh (1931), that the methods originally used by Putter
led to greatly overestimated levels of dissolved organic material. Never-
E. D. 5. CORNER AND ANTHONY 0 . DAVIES
B. Detritus
This fraction of the particulate material in the sea contains no
living plants or animals but includes bacteria, the faecal pellets and
cast moults of zooplankton and disintegrated phytoplankton cells.
Its capture by zooplankton has been deduced from examination of gut
contents. For example, Macdonald (1927) found that the guts of small
specimens of Meganyctiphanes norvegica (M. Sars) contained both
diatoms and I ‘ wet dust ”, i.e. flocculent detritus ; and Mauchlinc
(1960) found 20% by volume of “ grit ” and vegetable detritus in the
guts of Calanus jinmarchicus (Gunnerus) from deep water (150 m) in
the same sea area.
If detritus were a valuable diet for zooplankton, a large source of
food would be available to the animals, for Jsrgensen (1966) concludes
that of the total particulate material present in the sea generally only
10-20% by weight is represented by phytoplankton. However, the
nutritive value of detritus is by no means well established. Thus, so
far the only “ natural ” detritus tested is that obtained by Baylor and
Sutcliffe (1963), using material extracted from sea water by the action
of rising bubbles. The test animal was Artemia salina and the growth
rate of animals fed on detritus was compared with that of controls
either starved or fed on yeast. For the first four days animals given
detritus or yeast as a food had roughly the same growth rate, after
which that of animals fed on detritus was lower, although they continued to increase in size until the end of the sixteenth day. No measurements were made of the relative levels of the two diets, however, and to
establish the presence of dietary factors needed for reproduction would
require a much longer study, including attempts to rear the animals
through several generations. Moreover, Paffenhtifer and Strickland
(1970), studying an animal more representative of marine zooplankton,
found that natural detritus is not eaten by Calanus helgolandicus
(Claus), although the animal will apparently eat disintegrated samples
of its own faecal pellets, as well as “ dead ’’ diatom cells. It would be
interesting to know whether these two ingested forms of detritus have
any nutritive value.
C . Dissolved organic material
Putter (1909) was the first to claim that organic substances dissolved
in sea water may be absorbed and used by animals directly. However,
it has since become clear, mainly through the work of Moore et al.
(1912) and Krogh (1931), that the methods originally used by Putter
led to greatly overestimated levels of dissolved organic material. Never-